Is it accidental that IA to VIIA main group elements during chemical reactions get eight electrons in the outermost shells of their ions, similar to noble gas atoms?

No. It cannot be simply accidental. Eight electrons in the outermost shell definitely gives stability to the ion or atom. Based on the above observations a statement known as “ The Octet Rule” is framed.

It may be stated as “The atoms of elements tend to undergo chemical changes that help to leave their atoms with eight outer-shell electrons.”

Lewis depicted the atom in terms of a positively charged kernel (Kernel is the nucleus and all other electrons in the atom except the outer most shell electrons) and the outershell that could accommodate a maximum of eight electrons.

Chemically active elements do not have an octet of electrons in the valence shell of their atoms. Their reactivity arises from their tendency to achieve the octet, by forming bonds either with atoms of their own type or with atoms of other elements.

sThe force of attraction between any two atoms or a group of atoms that results a stable entity is called a ‘chemical bond’. There are many types of chemical bonds, but here we discuss only about ionic bond and covalent bond.

Kossel proposed the ionic bond (electrostatic bond) based on the following facts

i. Ionic bond is formed between atoms of two dissimilar elements due to transfer of electrons from the atom of one element to the other.

ii. There are highly reactive metals like alkali metals (IA) and highly reactive non-metals like halogens (VIIA) on the left side and right side of the periodic table respectively.

iii. Noble gases except helium have eight electrons in the valence shells of their atoms. They are chemically inactive and stable.

iv. To attain eight electrons in the outermost shell similar to noble gases metal atoms that have one two or three electrons in the valence shells generally lose those electrons and form stable positive ions called cations.